Imaging lens and imaging device provided with the same

ABSTRACT

An imaging lens substantially consists of five lenses consisting of, in order from the object side: a first lens having a positive refractive power with a convex surface toward the object side; a second lens having a negative refractive power and having a meniscus shape with a convex surface toward the image side; a third lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; a fourth lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; and a fifth lens having a negative refractive power, wherein an image-side surface of the fifth lens includes a concave surface and at least one inflection point, wherein a predetermined conditional expression is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-184914, filed on Sep. 6, 2013. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a fixed-focus imaging lens that forms an optical image of a subject on an image sensor, such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), and an imaging device that is provided with the imaging lens and performs imaging, such as an imaging device incorporated in a digital still camera, a mobile phone with camera, a PDA (Personal Digital Assistance), a smartphone, a tablet-type terminal, a portable video game player, etc.

Description of the Related Art

Along with the spread of personal computers in ordinary homes, etc., digital still cameras that are capable of inputting image information, such as photographed landscapes and portraits, to a personal computer are also rapidly spreading. Further, more and more mobile phones, smartphones and tablet-type terminals are equipped with a camera module for inputting images. The above-mentioned devices capable of imaging use an image sensor, such as a CCD or CMOS. In recent years, pixel density of such image sensors is also becoming higher, and imaging lenses with higher resolution and higher performance are demanded. For example, performance that can accommodate a high pixel density of 5 megapixel or more, or more preferably 8 megapixel or more is demanded.

In order to meet the above-described demands, an imaging lens formed by a relatively large number of lenses, namely, having a five-lens configuration may be provided. For example, each of Japanese Patent No. 4792605 and U.S. Patent Application Publication No. 20130057968 (hereinafter, Patent Documents 1 and 2, respectively) proposes an imaging lens with a five-lens configuration including, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power.

SUMMARY OF THE INVENTION

On the other hand, for an imaging lens for use, in particular, with devices that are becoming thinner and thinner, such as PDAs, smartphones and tablet-type terminals, it is desired to accomplish an imaging lens with a wide angle of view that is sufficient for accommodating a large-size image sensor that meets the demand for higher resolution. The imaging lens disclosed in Patent Document 1 has a narrow angle of view, and it is difficult, to apply this imaging lens to an image sensor that meets the demand for higher resolution. The imaging lens disclosed in Patent Document 2 has insufficiently corrected astigmatism and therefore the image plane largely fluctuates depending on the image height, and more uniform astigmatism correction is required across the entire image plane in which the image sensor is placed.

In view of the above-described circumstances, the present invention is directed to providing an imaging lens having a wide angle of view applicable to an image sensor that meets the demand for higher resolution, and capable of achieving high imaging performance throughout from the central angle of view to the peripheral angle of view, and an imaging device provided with the imaging lens and capable of capturing high-resolution images.

An aspect of the imaging lens of the invention is an imaging lens substantially consisting of five lenses consisting of, in order from an object side: a first lens having a positive refractive power with a convex surface toward the object side; a second lens having a negative refractive power and having a meniscus shape with a convex surface toward the image side; a third lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; a fourth lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; and a fifth lens having a negative refractive power, wherein an image-side surface of the fifth lens includes a concave surface and at least one inflection point, wherein the conditional expression below is satisfied: 1.15<f/f1<1.7  (1) where f is a focal length of the entire system, and f1 is a focal length of the first lens.

It should be noted that, with respect to the imaging lens of the invention, the expression “substantially consisting of five lenses” means that the imaging lens of the invention may include, in addition to the five lenses: lenses substantially without any power; optical elements other than lenses, such as a stop and a cover glass; mechanical components, such as a lens flange, a lens barrel, an image sensor, and a camera shake correcting mechanism; etc. It should be noted that the sign (positive or negative) with respect to the surface shape or the refractive power of any lens having an aspheric surface of the above-described lenses is about the paraxial region.

When the imaging lens of the invention further employs and satisfies the following preferred features, even higher optical performance can be achieved.

In the imaging lens of the invention, it is preferred that the first lens have a meniscus shape.

It is preferred that the imaging lens of the invention further include an aperture stop disposed on the object side of the object-side surface of the second lens.

In the imaging lens of the invention, it is preferred that the fifth lens have a biconcave shape.

It is preferred that the imaging lens of the invention satisfy any of the conditional expressions (1-1) to (7-1) below: 1.22<f/f1<1.6  (1-1), 1.25<f/f1<1.55  (1-2), −1.48<f/f45<0  (2), −1.25<f/f45<0  (2-1), −1.1<f/f45<−0.05  (2-2), −1.5<f12/f45<0  (3), −1.45<f12/f45<−0.05  (3-1), −0.3<f/f345<0.35  (4), −0.29<f/f345<0.2  (4-1), −0.95<f/f2<−0.65  (5), −0.9<f/f2<−0.68  (5-1), 0.05<f/f3<0.95  (6), 0.06<f/f3<0.9  (6-1), 0.48<f/f4<1.57  (7), and 0.5<f/f4<1.56  (7-1), where f is a focal length of the entire system, f1 is a focal length of the first lens, f2 is a focal length of the second lens, f3 is a focal length of the third lens, f4 is a focal length of the fourth lens, f12 is a combined focal length of the first lens and the second lens, f45 is a combined focal length of the fourth lens and the fifth lens, f345 is a combined focal length of the third to the fifth lenses. In preferred aspects of the invention, any one or any combination of the conditional expressions (1-1) to (7-1) may be satisfied.

The imaging device according to the invention comprises the imaging lens of the invention.

According to the imaging lens of the invention, which has the five lens configuration as a whole, the configuration of each lens element, in particular, the shape of each of the first to the fifth lenses is optimized, thereby accomplishing a lens system having a wide angle of view applicable to an image sensor that meets the demand for higher resolution, and having high imaging performance throughout from the central angle of view to the peripheral angle of view.

Further, the imaging device of the invention outputs an imaging signal according to an optical image formed by the imaging lens with high imaging performance of the invention, and therefore can capture high-resolution images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens sectional view illustrating a first configuration example of an imaging lens according to one embodiment of the invention and corresponding to Example 1,

FIG. 2 is a lens sectional view illustrating a second configuration example of the imaging lens according to one embodiment of the invention and corresponding to Example 2,

FIG. 3 is a lens sectional view illustrating a third configuration example of the imaging lens according to one embodiment of the invention and corresponding to Example 3,

FIG. 4 is a lens sectional view illustrating a fourth configuration example of the imaging lens according to one embodiment of the invention and corresponding to Example 4,

FIG. 5 is a lens sectional view illustrating a fifth configuration example of the imaging lens according to one embodiment of the invention and corresponding to Example 5,

FIG. 6 is a lens sectional view illustrating optical paths through the imaging lens shown in FIG. 1,

FIG. 7 is an aberration diagram showing various aberrations of the imaging lens according to Example 1 of the invention, where spherical aberration is shown at “A”, astigmatism (field curvature) is shown at “B”, distortion is shown at “C”, and lateral chromatic aberration is shown at “D”,

FIG. 8 is an aberration diagram showing various aberrations of the imaging lens according to Example 2 of the invention, where spherical aberration is shown at “A”, astigmatism (field curvature) is shown at “B”, distortion is shown at “C”, and lateral chromatic aberration is shown at “D”,

FIG. 9 is an aberration diagram showing various aberrations of the imaging lens according to Example 3 of the invention, where spherical aberration is shown at “A”, astigmatism (field curvature) is shown at “B”, distortion is shown at “C”, and lateral chromatic aberration is shown at “D”,

FIG. 10 is an aberration diagram showing various aberrations of the imaging lens according to Example 4 of the invention, where spherical aberration is shown at “A”, astigmatism (field curvature) is shown at “B”, distortion is shown at “C”, and lateral chromatic aberration is shown at “D”,

FIG. 11 is an aberration diagram showing various aberrations of the imaging lens according to Example 5 of the invention, where spherical aberration is shown at “A”, astigmatism, (field curvature) is shown at “B”, distortion is shown at “C”, and lateral chromatic aberration is shown at “D”,

FIG. 12 shows an imaging device in the form of a mobile phone terminal provided with the imaging lens according to the invention, and

FIG. 13 shows an imaging device in the form of a smartphone provided with the imaging lens according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first configuration example of an imaging lens according to a first embodiment of the invention. This configuration example corresponds to a lens configuration of a first numerical example (shown in Tables 1 and 2), which will be described later. Similarly, FIGS. 2 to 5 show cross-sectional configurations of second to fifth configuration examples corresponding to imaging lenses according to second to fifth embodiments, which will be described later. The second to fifth configuration examples correspond to lens configurations of second to fifth numerical examples (shown in Tables 3 to 10), which will be described later. In FIGS. 1 to 5, each symbol “Ri” denotes a radius of curvature of the i-th surface, where the most object-side surface of the lens elements is the first surface and the surface number is sequentially increased toward the image side (the formed image side), and each symbol “Di” denotes a surface distance between the i-th surface and the i+1-th surface along the optical axis Z. It should be noted that these configuration examples have the same basic configuration. Therefore the following description is made based on the configuration example of the imaging lens shown in FIG. 1, and the configuration examples shown in FIGS. 2 to 5 are described as necessary. FIG. 6 is a lens sectional view showing optical paths through the imaging lens L shown in FIG. 1. FIG. 6 shows optical paths of an axial bundle of rays 2 and a bundle of rays 3 at the maximum angle of view from an object point at infinity.

The imaging lens L according to each embodiment of the invention is preferably usable with various imaging devices using an image sensor, such as a CCD or CMOS, in particular, relatively small portable terminal devices, such as digital still cameras, mobile phones with camera, smartphones, tablet-type terminals and PDAs. The imaging lens L includes, in order from the object side along the optical axis Z1, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5.

FIG. 12 shows the appearance of a mobile phone terminal which is an imaging device 1 according to one embodiment of the invention. The imaging device 1 of the embodiment of the invention includes the imaging lens L of any of the embodiments of the invention, and an image sensor 100 (see FIG. 1), such as a CCD, for outputting an imaging signal according to an optical image formed by the imaging lens L. The image sensor 100 is placed in the image plane (image plane R14) of the imaging lens L.

FIG. 13 shows the appearance of a smartphone which is an imaging device 501 according to one embodiment of the invention. The imaging device 501 of the embodiment of the invention includes a camera unit 541 which includes the imaging lens L of any of the embodiments of the invention and an image sensor 100 (see FIG. 1), such as a CCD, for outputting an imaging signal according to an optical image formed by the imaging lens L. The image sensor 100 is placed in the image plane (image plane R14) of the imaging lens L.

Various optical members CG may be provided between the fifth lens L5 and the image sensor 100 depending on the configuration of the camera provided with the imaging lens L. For example, a cover glass for protecting the imaging area, and a flat plate-like optical member, such as an infrared cut-off filter, may be provided between the fifth lens L5 and the image sensor 100. In this case, for example, a flat plate-like cover glass with a coating having a filter effect, such as an effect of an infrared cut-off filter or ND filter, or a material having the same effect may be used as the optical member CG.

Alternatively, without using any optical member CG, the fifth lens L5 may be provided with a coating having the same effect as the optical member CG, for example. This allows reduction of the number of parts forming the lens and the entire length of the lens.

It is preferred that the imaging lens L include an aperture stop St disposed on the object side of the object-side surface of the second lens L2. Disposing the aperture stop St on the object side of the object-side surface of the second lens L2 in this manner allows minimizing increase of the incidence angle of rays traveling through the optical system on the image plane (the image sensor), in particular, at the marginal area of the imaging area. It should be noted that the description “disposed on the object side of the object-side surface of the second lens L2” means that the position of the aperture stop St along the optical axis direction is the same position as the intersection between a marginal axial ray and the object-side surface of the second lens L2 or a position nearer to the object side than the intersection. Alternatively, the aperture stop St may be disposed between the first lens L1 and the second lens L2 along the optical axis direction, as with the imaging lens L according to each embodiment. In this case, successful correction of field curvature can be achieved.

In this imaging lens L, the first lens L1 has a positive refractive power in the vicinity of the optical axis, and has a convex surface toward the object side in the vicinity of the optical axis. When the first lens L1, which accounts for a major part of the imaging function, has a shape with a convex surface toward the object side in the vicinity of the optical axis, the first lens L1 has a sufficient positive refractive power, and this preferably allows reduction of the entire length of the lens. Further, it is preferred that the first lens L1 have a meniscus shape with the concave surface toward the image side in the vicinity of the optical axis. In this case, the position of the posterior principal point of the first lens L1 can be made nearer to the object side, and this preferably allows reduction of the entire length of the lens.

The second lens L2 has a negative refractive power in the vicinity of the optical axis. This allows achieving successful correction of spherical aberration and longitudinal chromatic aberration that occur when rays travel through the first lens L1. Further, the second lens L2 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis. When the second lens L2 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis, the position of the posterior principal, point of the second lens L2 can be made nearer to the object side, and this preferably allows reduction of the entire length of the lens.

The third lens L3 has a positive refractive power in the vicinity of the optical axis. This preferably allows correcting spherical aberration. Further, the third lens L3 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis. When the third lens L3 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis, astigmatism can preferably be minimized, and this makes it easier to achieve a wider angle of view.

The fourth lens L4 has a positive refractive power in the vicinity of the optical axis. This preferably allows minimizing increase of the incidence angle of rays traveling through the optical system on the image plane (the image sensor), in particular, at an intermediate angle of view. Further, the fourth lens L4 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis. When the fourth lens L4 has a meniscus shape with the convex surface toward the image side in the vicinity of the optical axis, incidence angle on the object-side surface of the fourth lens L4 can be reduced, and this allows minimizing various aberrations. This preferably allows correcting distortion, lateral chromatic aberration and astigmatism, which tend to occur along with reduction of the entire length of the lens.

The fifth lens L5 has a negative refractive power in the vicinity of the optical axis. Regarding the first to the fourth lenses L1 to L4 as one positive optical system, the fifth lens L5 having a negative refractive power makes the imaging lens L as a whole a telephoto configuration. This allows making the position of the posterior principal point of the entire imaging lens L nearer to the object side, thereby preferably allowing reduction of the entire length of the lens.

Further, as shown in the first to the fifth embodiments, it is preferred that the fifth lens L5 have a biconcave shape in the vicinity of the optical axis. In this case, a sufficiently strong negative refractive power of the fifth lens L5 can be achieved while minimizing increase of the absolute value of the curvature of each surface of the fifth lens L5. Further, the fifth lens L5 having a biconcave shape in the vicinity of the optical axis allows successful correction of field curvature.

Still further, as shown in the first to the fifth embodiments, it is preferred that the fifth lens L5 have a concave surface toward the image side in the vicinity of the optical axis, and the image-side surface of the fifth lens L5 have an aspheric shape having at least one inflection point. In this case, increase of the incidence angle of rays traveling through the optical system on the image plane (the image sensor), in particular, at the marginal area of the imaging area can be minimized. It should be noted that the “inflection point” of the image-side surface of the fifth lens L5 refers to a point where the shape of the image-side surface of the fifth lens L5 changes from a convex shape to a concave shape (or from a concave shape to a convex shape) toward the image side. The position of the inflection point can be any position within an effective radius of the image-side surface of the fifth lens L5 along the radial direction from the optical axis.

According to the above-described imaging lens L, which has the five lens configuration as a whole, the configuration of each of the lens elements, the first to the fifth lenses L1 to L5, is optimized, thereby accomplishing a lens system having a wide angle of view applicable to an image sensor that meets the demand for higher resolution, and having high imaging performance throughout from the central angle of view to the peripheral angle of view.

In order to achieve even higher performance, it is preferred that each of the first to the fifth lenses L1 to L5 of the imaging lens L have an aspheric surface on at least one side thereof.

Further, it is preferred that each of the lenses L1 so L5 forming the imaging lens L be a single lens rather than a cemented lens. In this case, the number of aspheric surfaces is greater than that in a case where any of the lenses L1 to L5 are cemented together to form a cemented lens. This allows higher freedom of design of each lens, thereby preferably allowing reduction of the entire length of the lens.

Still further, in a case where the lens configuration of each of the first to the fifth lenses L1 to L5 forming the imaging lens L is set to provide, for example, a full angle of view of 69° or more, as with the imaging lenses according to the first to the fifth embodiment, the imaging lens L is preferably applicable to an image sensor having a size that meets the demand for higher resolution and incorporated in a mobile phone, or the like. In contrast, the lens system disclosed in Patent Document 1 has a full angle of view of around 64°, and it is difficult to apply this lens system to an image sensor having a size that meets the demand for higher resolution incorporated in a mobile phone, or the like.

Next, operation and effects related to conditional expressions of the imaging lens L having the above-described configuration are described in more detail. It is preferred that the imaging lens L satisfy any one or any combination of she conditional express ions described below. It is preferred that one or more conditional expressions to be satisfied are selected as appropriate depending on requirements on the imaging lens L.

First, it is more preferred that a focal length f1 of the first lens L1 and a focal length f of the entire system satisfy the conditional expression (1) below: 1.15<f/f1<1.7  (1).

The conditional expression (1) defines a preferred numerical range of the ratio of the focal length f of the entire system to the focal length f1 of the first lens L1. When the refractive power of the first lens L1 is ensured such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (1), the positive refractive power of the first lens L1 does not become excessively weak relative to the refractive power of the entire system, and reduction of the entire length of the lens can preferably be achieved while successfully correcting aberrations. When the refractive power of the first lens L1 is maintained such that the ratio does not become greater than or equal to the upper limit of the conditional expression (1), the positive refractive power of the first lens L1 does not become excessively strong relative to the refractive power of the entire system, and successful correction of spherical aberration and astigmatism, in particular, can be achieved. In order to enhance this effect, it is more preferred that the conditional expression (1-1) below be satisfied, or it is even more preferred that the conditional expression (1-2) below be satisfied: 1.22<f/f1<1.6  (1-1), or 1.25<f/f1<1.55  (1-2).

It is preferred that a combined focal length f45 of the fourth lens L4 and the fifth lens L5 and the focal length f of the entire system satisfy the conditional expression (2) below: −1.48<f/f45<0  (2).

The conditional expression (2) defines a preferred numerical range of the ratio of the focal length f of the entire system to the combined focal length f45 of the fourth lens L4 and the fifth lens L5. When the combined focal length f45 of the fourth lens LA and the fifth lens L5 is maintained such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (2), the negative refractive power of the lens group consisting of the fourth lens L4 and the fifth lens L5 does not become excessively strong relative to the refractive power of the entire system, and it is not necessary to excessively increase the positive refractive power of the lens group consisting of the first to the third lenses L1 to L3, thereby allowing minimizing high-order spherical aberration. This preferably allows reduction of the entire length of the lens and achieving high resolution performance. When the combined focal length f45 of the fourth lens L4 and the fifth lens L5 is ensured such that the ratio does not become greater than or equal to the upper limit of the conditional expression (2), the negative refractive power of the lens group consisting of the fourth lens L4 and the fifth lens L5 disposed at mage-side positions in the imaging lens L does not become excessively weak relative to the refractive power of the entire system, and this is advantageous for reduction of the entire length of the lens. In order to enhance this effect, it is more preferred that the conditional expression (2-1) below be satisfied, or it is even more preferred that the conditional expression (2-2) below be satisfied: −1.25<f/f45<0  (2-1), or −1.1<f/f45<−0.05  (2-2).

It is preferred that a combined focal length 112 of the first lens L1 and the second lens L2 and the combined focal length f45 of the fourth lens L4 and the fifth lens L5 satisfy the conditional expression (3) below: −1.5<f12/f45<0  (3).

The conditional expression (3) defines a preferred numerical range of the ratio of the combined focal length f12 of the first lens L1 and the second lens L2 to the combined focal length f45 of the fourth lens L4 and the fifth lens L5. When the combined focal length f45 of the fourth lens L4 and the fifth lens L5 is maintained such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (3), the refractive power of the lens group consisting of the fourth lens L4 and the fifth lens L5 does not become excessively strong relative to the refractive power of the lens group consisting of the first lens L1 and the second lens L2, and this allow minimizing insufficient correction of field curvature. When the combined focal length f45 of the fourth lens L4 and the fifth lens L5 is ensured such that the ratio does not become greater than or equal to the upper limit of the conditional expression (3), the refractive power of the lens group consisting of the fourth lens LA and the fifth lens L5 does not become excessively weak relative to the refractive power of the lens group consisting of the first lens L1 and the second lens L2, and this is advantageous for reduction of the entire length of the lens. In order to enhance this effect, it is more preferred that the conditional expression (3-1) below be satisfied, or it is even more preferred that the conditional expression (3-2) below be satisfied: −1.45<f12/f45<−0.05  (3-1), or −1.4<f12/f45<−0.1  (3-2).

It is preferred that a combined focal length f345 of the third to the fifth lenses L3 to L5 and the focal length f of the entire system satisfy the conditional expression (4) below: −0.3<f/f345<0.35  (4).

The conditional expression (4) defines a preferred numerical range of the ratio of the focal length f of the entire system to the combined focal length f345 of the third to the fifth lenses L3 to L5. When the combined focal length f345 of the third to the fifth lenses L3 to L5 is maintained such that the ratio does not become smaller er than or equal to the lower limit of the conditional expression (4), the refractive power of the lens group consisting of the third to the fifth lenses L3 to L5 does not become excessively strong relative to the refractive power of the entire system, and this allows minimizing increase of the incidence angle of rays traveling through the optical system on the image plane (the image sensor), in particular, at an intermediate angle of view. When she combined focal length f345 of the third to the fifth lenses L3 to L5 is maintained such that the ratio does not become greater than or equal to the upper limit of the conditional expression (4), the refractive power of the lens group consisting of the third to the fifth lenses L3 to L5 does not become excessively strong relative to she refractive power of the entire system, and this preferably allows reduction of the entire length of the lens. In order to enhance this effect, it is more preferred that she conditional expression (4-1) below be satisfied, or it is even more preferred that the conditional expression (4-2) below be satisfied: −0.29<f/f345<0.2  (4-1), or −0.28<f/f345<0.1  (4-2).

It is more preferred that a focal length f2 of the second lens L2 and the focal length f of the entire system satisfy the conditional expression (5) below: −0.95<f/f2<−0.65  (5).

The conditional expression (5) defines a preferred numerical range of the ratio of the focal length f of the entire system to the focal length f2 of the second lens L2. When the refractive power of the second lens L2 is maintained such chat she ratio does not become smaller than or equal to the lower limit, of the conditional expression (5), the negative refractive power of the second lens L2 does not become excessively strong relative to the refractive power of the entire system, and this preferably allows reduction of the entire length of the lens. When the refractive power of the second lens L2 is ensured such that the ratio does not become greater than or equal to the upper limit of the conditional expression (5), the negative refractive power of the second lens L2 does not become excessively weak relative to the refractive power of the entire system, and this allows successful correction of, in particular, axial chromatic aberration. In order to enhance this effect, it is more preferred that the conditional expression (5-1) below be satisfied: −0.9<f/f2<−0.68  (5-1).

It is more preferred that a focal length f3 of the third lens L3 and the focal length f of the entire system satisfy the conditional expression (6) below: 0.05<f/f3<0.95  (6).

The conditional expression (6) defines a preferred numerical range of the ratio of the focal length f of the entire system to the focal length f3 of the third lens L3. When the refractive power of the third lens L3 is ensured such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (6), the positive refractive power of the third lens L3 does not become excessively weak relative to the refractive power of the entire system, and this preferably allows reduction of the entire length of the lens. When the refractive power of the third lens L3 is maintained such that the ratio does not become greater than or equal to the upper limit of the conditional expression (6), the positive refractive power of the third lens L3 does not become excessively strong relative to the refractive power of the entire system, and this allows successful correction of spherical aberration. In order to enhance this effect, it is more preferred that the conditional expression (6-1) below be satisfied, or it is even more preferred that the conditional expression (6-2) below be satisfied: 0.06<f/f3<0.9  (6-1), or 0.1<f/f3<0.7  (6-2).

It is more preferred that a focal length f4 of the fourth lens L4 and the focal length f of the entire system satisfy the conditional expression (7) below: 0.48<f/f4<1.57  (7).

The conditional expression (7) defines a preferred numerical range of the ratio of the focal length f of the entire system to the focal length f4 of the fourth lens L4. When the refractive power of the fourth lens L4 is ensured such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (7), the positive refractive power of the fourth lens L4 does not become excessively weak relative to the refractive power of the entire system, and this allows minimizing increase of the incidence angle of rays traveling through the optical system on the image plane (the image sensor), in particular, at an intermediate angle of view. Also, when the refractive power of the fourth lens L4 is ensured such that the ratio does not become smaller than or equal to the lower limit of the conditional expression (7), correction of distortion and lateral chromatic aberration can preferably be achieved. When the refractive power of the fourth lens L4 is maintained such that the ratio does not become greater than or equal to the upper limit of the conditional expression (7), the positive refractive power of the fourth lens LA does not become excessively strong relative to the refractive power of the entire system, and this allows successful correction of, in particular, spherical aberration and astigmatism. In order to enhance this effect, it is more preferred that the conditional expression (7-1) below be satisfied: 0.5<f/f4<1.56  (7-1).

As described above, according to the imaging lens L of the embodiments of the invention, which has the five lens configuration as a whole, the configuration of each lens element is optimized, thereby accomplishing a lens system having a wide angle of view and having high imaging performance throughout from the central angle of view to the peripheral angle of view.

The imaging lens according to the embodiments of the invention can achieve even higher imaging performance by satisfying the above-described preferred conditions, as appropriate. The imaging device according to the embodiments of the invention outputs an imaging signal according to an optical image formed by the high-performance imaging lens of the embodiments of the invention, and therefore can capture a high-resolution image throughout from the central angle of view to the peripheral angle of view.

Next, specific numerical examples of the imaging lens according to the embodiments of the invention are described. In the following description, several numerical examples are explained, at once.

Tables 1 and 2 presented below show specific lens data corresponding to the configuration of the imaging lens shown in FIG. 1. Specifically, Table 1 shows basic lens data, and Table 2 shows data about aspheric surfaces. The lens data shown in Table 1 is the lens data of the imaging lens according to Example 1, and each value in the column of surface number “Si” is the surface number of the i-th surface, where the most object-side surface of the lens elements is the 1st surface (the aperture stop St is the 3rd surface) and the number is sequentially increased toward the image side. Each value in the column of radius of curvature “Ri”, which corresponds to each symbol “Ri” shown in FIG. 1, is the value (mm) of radius of curvature of the i-th surface from the object side. Each value in the column of surface distance “Di” is the surface distance (mm) between the i-th surface Si and the i+1-th surface Si+1 from the object side along the optical axis Z. Each value in the column of “Ndj” is the value of refractive index with respect to the d-line (587.6 nm) of the j-th optical element from the object side. Each value in the column of “νdj” is the value of Abbe number with respect to the d-line of the j-th element from the object side. It should be noted chat the lens data also shows values the focal length f (mm) and the back focus Bf (mm) of the entire system. It should be noted that the value of the back focus Bf is an equivalent air distance.

Each of the first to the fifth lenses L1 to L5 of the imaging lens according to Example 1 has aspheric surfaces on both sides. The value of radius of curvature of each aspheric surface in the basic lens data shown in Table 1 is a value of radius of curvature in the vicinity of the optical axis (paraxial radius of curvature).

Table 2 shows aspheric surface data of the imaging lens of Example 1. In each value shown as the aspheric surface data, the symbol “E” means that the numerical value following the symbol. “E” is an exponent with the base being 10, and that the numerical value before the symbol “E” is multiplied by the numerical value represented by the exponential function with the base being 10. For example, “1.0E−02” means “1.0×10⁻²”.

As the aspheric surface data, values of coefficients Ai and KA in the formula of aspheric shape expressed as the formula (A) below are shown. More specifically, Z represents a length (mm) of a perpendicular line from a point on the aspheric surface at a height h from the optical axis to a plane (a plane perpendicular to the optical axis) tangential to the apex of the aspheric surface. Z=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAi·h ^(i)  (A), where Z is a depth (mm) of the aspheric surface, h is a distance (mm) from the optical axis to the lens surface (height), C is a paraxial curvature=1/R (where F is a paraxial radius of curvature), Ai is an i-th order (where i is an integer of 3 or more) aspheric coefficient, and KA is an aspheric coefficient.

Similarly to the lens data of the imaging lens of Example 1, specific lens data corresponding to the configurations of imaging lenses shown in FIGS. 2 to 5 are shown as Examples 2 to 5 in Tables 3 to 10. In the imaging lenses according to Example 1 to 5, each of the first to the fifth lenses L1 to L5 has aspheric surfaces on both sides.

FIG. 7 shows, at “A” to “D”, aberration diagrams of spherical aberration, astigmatism, distortion, and lateral chromatic aberration (chromatic aberration of magnification), respectively, of the imaging lens of Example 1. Each aberration shown in the aberration diagrams, of spherical aberration, astigmatism (field curvature), and distortion is with respect to the d-line (the wavelength of 587.6 nm) used as the reference wavelength. The aberration diagrams of spherical aberration and lateral chromatic aberration also show the aberrations with respect to the F-line (the wavelength of 486.1 nm) and the C-line (the wavelength of 656.3 nm). The aberration diagram of spherical aberration also shows the aberration with respect to the g-line (the wavelength of 435.8 nm). In the aberration diagram of astigmatism, the aberration in the sagittal direction (S) is shown in the solid line and the aberration in the tangential direction (T) is shown in the dotted line. The symbol “Fno.” means “F-number” and the symbol “ω” means “half angle of view”.

Similarly, the various aberrations of the imaging lenses of Examples 2 to 5 are shown at “A” to “D” in FIGS. 8 to 11.

Further, Table 11 shows values relating to the conditional expressions (1) so (7) according to the invention for each of Examples 1 to 5.

As can be seen from the numerical data and the aberration diagrams, an imaging lens having large image size and high imaging performance is accomplished in each example while achieving reduction of the entire length of the lens.

It should be noted that the numerical values shown in the above-described tables are rounded at predetermined decimal places. The unit of the values of angle is degrees and the unit of the values of length is millimeters; however, this is only one example, and any other suitable units may be used since optical systems are usable when they are proportionally enlarged or reduced.

It should be noted that the imaging lens of the invention is not limited to the above-described embodiments and examples, and various medications may be made to the invention when the invention is carried out. For example, the values of the radius of curvature, she surface distance, the refractive index, the Abbe number, the aspheric coefficients, etc., of each lens component are not limited to the values shown in the numerical examples and may take different values.

Further, while the imaging lenses of the above-described examples are described on the assumption that they are used as fixed-focus lenses, the imaging lens of the invention can be configured to allow focusing. For example, automatic focusing can be achieved by moving the entire lens system or moving part of the lenses forming the lens system along the optical axis.

TABLE 1 Example 1 f = 3.962, Bf = 0.913 Si Ri Di Ndj νdj *1 1.33064 0.500 1.54488 54.87 *2 13.50053 0.042 3 (aperture stop) ∞ 0.155 *4 −3.33976 0.265 1.63351 23.63 *5 −649.35066 0.446 *6 −809.65153 0.374 1.54488 54.87 *7 −17.22972 0.294 *8 −3.77178 0.757 1.54488 54.87 *9 −1.14081 0.436 *10  −2.15591 0.265 1.54488 54.87 *11  2.18996 0.516 12 ∞ 0.221 1.51633 64.14 13 ∞ 0.251 14 (image plane) ∞ *aspheric surface

TABLE 2 Example 1: Aspheric Surface Data Surface No. KA A3 A4 A5 A6 1 −5.9278839E−01 0.0000000E+00  1.7181445E−01 −6.7297590E−01 2.3794323E+00 2 −3.8118045E+00 0.0000000E+00  4.2811630E−02  4.4070533E−03 −7.9523517E−01  4 −1.8469116E+01 0.0000000E+00  1.2582355E−01 −3.3200820E−01 1.2424368E+00 5 −9.6355821E+00 0.0000000E+00  2.7849756E−01 −6.3875661E−01 2.0317040E+00 6  3.4586284E−05 0.0000000E+00 −1.0593717E−01 −2.0037841E−01 4.3290514E−01 7  2.1724297E+00 0.0000000E+00 −4.1303919E−02 −3.8958501E−01 6.9504264E−01 8  9.8273296E+00 0.0000000E+00  1.3048449E−01 −7.5003828E−01 1.9015853E+00 9 −3.8659497E−01 0.0000000E+00  1.6410367E−01 −1.6387110E−01 2.3310472E−01 10 −3.7880303E+00 0.0000000E+00 −2.3872783E−02  6.2217736E−02 −2.0367155E−01  11 −9.1067368E+00 0.0000000E+00 −2.1582348E−01  2.9945632E−01 −2.6475285E−01  A7 A8 A9 1 −4.0531393E+00 3.4172468E+00 −1.1043925E+00 2  2.4958470E+00 −2.9233977E+00   1.2005436E+00 4 −2.6436830E+00 2.9087311E+00 −1.3390643E+00 5 −3.1778997E+00 2.3701858E+00 −5.8073606E−01 6 −6.1117555E−01 4.6108234E−01 −2.1473309E−01 7 −8.7147832E−01 6.0311251E−01 −2.1163043E−01 8 −2.5452045E+00 1.6608933E+00 −4.3025696E−01 9 −3.8474995E−01 2.9843563E−01 −8.4775065E−02 10  1.6400758E−01 −5.2953849E−02   7.4028762E−03 11  1.4537633E−01 −4.7432079E−02   6.9709738E−03

TABLE 3 Example 2 f = 3.873, Bf = 0.998 Si Ri Di Ndj νdj *1 1.38523 0.402 1.54488 54.87 *2 78.20209 0.030 3 (aperture stop) ∞ 0.123 *4 −2.84560 0.201 1.63351 23.63 *5 −647.01733 0.349 *6 −399.82529 0.415 1.54468 54.87 *7 −14.82878 0.410 *8 −3.71689 0.933 1.54488 54.87 *9 −1.08574 0.538 *10  −2.33594 0.205 1.54488 54.87 *11  2.07912 0.704 12 ∞ 0.221 1.51633 64.14 13 ∞ 0.148 14 (image plane) ∞ *aspheric surface

TABLE 4 Example 2: Aspheric Surface Data Surface No. KA A3 A4 A5 A6 1 −5.6989038E−01 0.0000000E+00  1.6024195E−01 −5.7139834E−01 2.1256196E+00 2 −3.7490908E+00 0.0000000E+00  1.4155560E−02  1.9479007E−01 −1.0302837E+00  4 −1.8340017E+01 0.0000000E+00  1.2210374E−01 −3.4912636E−01 1.3567632E+00 5 −9.9648431E+00 0.0000000E+00  2.4607213E−01 −7.3472295E−01 2.2044235E+00 6  1.6788334E−01 0.0000000E+00 −2.5353501E−01 −9.6251250E−02 3.3872388E−01 7  2.1691855E+00 0.0000000E+00 −1.0567999E−01 −3.2645781E−01 7.3213891E−01 8  9.5292769E+00 0.0000000E+00  1.0468312E−01 −7.0940791E−01 1.9236509E+00 9 −4.2104387E−05 0.0000000E+00  1.5888689E−01 −1.3462654E−01 2.3782569E−01 10 −3.3569942E+00 0.0000000E+00 −7.3412083E−06  7.4678412E−02 −2.0829489E−01  11 −8.2184324E+00 0.0000000E+00 −1.8642261E−01  2.8003792E−01 −2.6255676E−01  A7 A8 A9 1 −3.9299360E+00 3.7207938E+00 −1.4046761E+00 2  2.3428763E+00 −2.4748994E+00   9.7516168E−01 4 −2.6825252E+00 2.4770995E+00 −8.1187251E−01 5 −3.2341436E+00 1.9603623E+00 −1.2898062E−01 6 −7.0218712E−01 4.2299704E−01 −8.3666042E−02 7 −9.2383164E−01 5.3052728E−01 −9.3830520E−02 8 −2.5402383E+00 1.6686923E+00 −4.3268064E−01 9 −3.8795888E−01 3.0093923E−01 −8.5165832E−02 10  1.6060268E−01 −5.3465095E−02   7.6412862E−03 11  1.4735754E−01 −4.7054717E−02   6.5915996E−03

TABLE 5 Example 3 f = 4.206, Bf = 0.619 Si Ri Di Ndj νdj *1 1.53406 0.440 1.54488 54.87 *2 238.65781 0.042 3 (aperture stop) ∞ 0.155 *4 −2.96613 0.200 1.63351 23.63 *5 −759.80458 0.403 *6 −664.50068 0.537 1.54488 54.87 *7 −3.95955 0.466 *8 −2.70063 0.673 1.54488 54.87 *9 −1.79191 0.990 *10  −1.88428 0.200 1.54488 54.87 *11  5.48900 0.324 12 ∞ 0.221 1.51633 64.14 13 ∞ 0.149 14 (image plane) ∞ *aspheric surface

TABLE 6 Example 3: Aspheric Surface Data Surface No. KA A3 A4 A5 A6 1 −6.6743609E−01 0.0000000E+00  1.0899521E−01 −2.2929190E−01 5.9133435E−01 2 −3.2005614E+00 0.0000000E+00 −1.8833678E−04  1.9145208E−01 −6.4692458E−01  4 −1.6630169E+01 0.0000000E+00  5.4942037E−02  2.2208239E−01 −6.0925697E−01  5  4.9999992E+01 0.0000000E+00  2.4507840E−01 −5.9545797E−01 1.7086889E+00 6  1.0000009E+01 0.0000000E+00 −1.0412856E−01 −1.9261653E−01 4.4038884E−01 7  6.2964296E−01 0.0000000E+00 −1.0759232E−01 −2.3308625E−01 6.8227317E−01 8  5.2145846E+00 0.0000000E+00 −1.3597497E−02 −5.0834909E−01 1.5418859E+00 9 −3.6638218E−01 0.0000000E+00 −2.0560492E−02 −9.9743182E−02 3.1416827E−01 10 −5.5038738E+00 0.0000000E+00 −3.9556154E−01  3.9329205E−01 −1.6565349E−01  11 −9.8708388E+00 0.0000000E+00 −3.3750506E−01  4.6205230E−01 −3.1898802E−01  A7 A8 A9 1 −7.0084991E−01 3.9278956E−01 −5.6994481E−02 2  1.0544654E+00 −8.2799922E−01   2.5229977E−01 4  5.7762477E−01 −9.5799443E−02  −9.7930725E−02 5 −2.6366571E+00 1.9688045E+00 −4.5884900E−01 6 −3.8059883E−01 −8.5993869E−02   2.4303519E−01 7 −1.0608557E+00 8.2955756E−01 −2.4111249E−01 8 −2.3526786E+00 1.8336907E+00 −5.4268502E−01 9 −4.6557181E−01 3.4760375E−01 −9.8202444E−02 10  1.0766008E−01 −9.4354031E−02   2.7657063E−02 11  1.3786157E−01 −4.0477550E−02   5.8794457E−03

TABLE 7 Example 4 f = 3.843, Bf = 0.886 Si Ri Di Ndj νdj *1 1.40487 0.500 1.54488 54.87 *2 10.64452 0.042 3 (aperture stop) ∞ 0.155 *4 −4.05967 0.265 1.63351 23.63 *5 −25.00949 0.446 *6 −24.63832 0.374 1.54488 54.87 *7 −5.74843 0.294 *8 −2.11713 0.757 1.54488 54.87 *9 −0.95977 0.436 *10  −1.53070 0.265 1.53500 56.30 *11  2.71738 0.516 12 ∞ 0.221 1.51633 64.14 13 ∞ 0.224 14 (image plane) ∞ *aspheric surface

TABLE 8 Example 4: Aspheric Surface Data Surface No. KA A3 A4 A5 A6 1 −3.7580800E+00 0.0000000E+00  2.4676693E−01 −5.7779345E−01 2.3965663E+00 2 −3.7995220E+00 0.0000000E+00 −2.3501158E−03  1.6685314E−01 −1.2803800E+00  4 −1.6577209E+01 0.0000000E+00  4.6757849E−02 −3.9904248E−01 2.0015108E+00 5  4.9358284E+01 0.0000000E+00  8.0754528E−02 −1.1426275E−01 1.1423935E+00 6 −1.2558562E+00 0.0000000E+00  9.6517286E−02 −1.1374725E+00 1.9318996E+00 7 −5.1741624E+00 0.0000000E+00  1.5367160E−02 −6.6291823E−01 9.9473283E−01 8  3.3294331E+00 0.0000000E+00  9.1614728E−02 −9.1730629E−01 2.0405352E+00 9 −1.9000003E+00 0.0000000E+00 −1.0889964E−01 −8.7164491E−02 2.9570760E−01 10 −5.7559693E+00 0.0000000E+00 −3.1006858E−02  1.0290361E−01 −2.3500704E−01  11 −1.1497464E+01 0.0000000E+00 −1.1899721E−01  2.1097949E−01 −2.4828746E−01  A7 A8 A9 1 −4.8746537E+00 4.5569330E+00 −1.6294026E+00 2  2.8342783E+00 −2.6778318E+00   9.2847769E−01 4 −4.4439699E+00 5.0320797E+00 −2.2394281E+00 5 −2.9521539E+00 3.6551310E+00 −1.6668081E+00 6 −1.1635376E+00 −4.0223493E−01   5.0215195E−01 7 −7.3743815E−01 2.4841946E−01 −2.1350083E−02 8 −2.3699382E+00 1.6349665E+00 −4.8336805E−01 9 −3.5649351E−01 2.8163009E−01 −9.2747862E−02 10  1.6803121E−01 −4.8558591E−02   5.4963344E−03 11  1.5330832E−01 −4.8572159E−02   6.2074606E−03

TABLE 9 Example 5 f = 3.865, Bf = 0.914 Si Ri Di Ndj νdj *1 1.37486 0.618 1.54488 54.87 *2 10.04697 0.216 3 (aperture stop) ∞ 0.042 *4 −4.33499 0.265 1.63351 23.63 *5 −23.99267 0.457 *6 −11.39922 0.326 1.54488 54.87 *7 −9.87457 0.326 *8 −2.00450 0.459 1.54488 54.87 *9 −1.09745 0.230 *10  240.48300 0.458 1.53500 56.30 *11  1.46297 0.516 12 ∞ 0.221 1.51633 64.14 13 ∞ 0.252 14 (image plane) ∞ *aspheric surface

TABLE 10 Example 5: Aspheric Surface Data Surface No. KA A3 A4 A5 A6 1 −3.7580800E+00 0.0000000E+00  2.4676693E−01 −5.7779345E−01 2.3965663E+00 2 −2.8905078E−06 0.0000000E+00  3.3522430E−03  2.1492051E−01 −1.3842029E+00  4 −1.9105551E+01 0.0000000E+00  8.8609243E−02 −3.6976981E−01 1.9053994E+00 5 −5.0693599E+01 0.0000000E+00  8.5405587E−02  3.0184724E−02 9.5271678E−01 6 −4.0978009E+00 0.0000000E+00  9.4562452E−02 −1.1544343E+00 1.8970906E+00 7  2.8218927E+01 0.0000000E+00 −9.5476845E−02 −6.2743253E−01 1.0615214E+00 8  3.3499984E+00 0.0000000E+00 −5.2584168E−02 −8.6231398E−01 2.0382911E+00 9 −1.5458004E+00 0.0000000E+00 −6.3239908E−02 −9.4335096E−02 2.9653984E−01 10 −8.2000184E+00 0.0000000E+00 −2.6623440E−02  1.0720610E−01 −2.3310550E−01  11 −5.1344724E+00 0.0000000E+00 −1.2758255E−01  2.1718113E−01 −2.4903715E−01  A7 A8 A9 1 −4.8746537E+00 4.5569330E+00 −1.6294026E+00 2  2.8328474E+00 −2.5112471E+00   7.7661571E−01 4 −4.5788090E+00 5.1780600E+00 −2.2072044E+00 5 −3.1317261E+00 4.0336277E+00 −1.8671613E+00 6 −1.0402069E+00 −3.7947331E−01   3.6044139E−01 7 −7.7911072E−01 2.1386936E−01 −3.8267252E−03 8 −2.3519525E+00 1.6316045E+00 −5.0060551E−01 9 −3.5923521E−01 2.7791960E−01 −9.9183052E−02 10  1.6845862E−01 −4.8786357E−02   4.9299152E−03 11  1.5355120E−01 −4.8309632E−02   6.1315027E−03

TABLE 11 Values Relating to Conditional Expressions Exam- Exam- Exam- Conditional ple ple ple No. Expression 1 2 3 Example 4 Example 5 1 f/f1 1.48 1.50 1.49 1.32 1.36 2 f/f45 −0.33 −0.10 −1.03 −0.54 −0.30 3 f12/f45 −0.37 −0.13 −1.39 −0.59 −0.30 4 f/f345 −0.18 0.07 −0.17 −0.20 −0.26 5 f/f2 −0.75 −0.86 −0.89 −0.50 −0.46 6 f/f3 0.12 0.14 0.58 0.28 0.03 7 f/f4 1.45 1.55 0.54 1.47 1.02

It should be noted that the above-described values of the paraxial radius of curvature, the surface distance, the refractive index, and the Abbe number were obtained by measurement performed by an expert in optical measurement according to the following methods.

The paraxial radius of curvature is obtained by measuring each lens using an ultra-high precision three-dimensional measuring device, UA3P (available from Panasonic Factory Solutions Co., Ltd.), and using the following procedure. Tentative values of a paraxial radius of curvature R_(m) (where m is a natural number) and a conic constant K_(m) are set and inputted to the UA3P, and an n-th order aspheric coefficient. An in the formula of aspheric shape is calculated from the tentative values and the measurement data using a fitting function attached to the UA3P. It is assumed that C=1/R_(m), and KA=K_(m)−1 in the above-described formula (A) of aspheric shape. Based on R_(m), K_(m), An, and the formula of aspheric shape, the depth Z of the aspheric surface in the optical axis direction depending on the height h from the optical axis is calculated. Then, for each height h from the optical axis, a difference between the calculated depth Z and the measured depth value Z′ is calculated, and whether or not the difference is within a predetermined range is determined. If it is determined that the difference is within the predetermined range, the set value of R_(m) is used as the paraxial radius of curvature. On the other hand, if the difference is out of the predetermined range, R_(m+1) and K_(m+1) are set by changing at least one of the values of R_(m) and K_(m) used to calculate the difference, and are inputted to the UA3P to perform the above-described calculations, and then, for each height it from the optical axis, whether or not a difference between the calculated depth Z and the measured depth value Z′ is within the predetermined range is determined. This operation is repeated until the difference between the calculated depth Z and the measured depth value Z′ for each height h from the optical axis falls within the predetermined range. It should be noted that the predetermined range here is within 200 nm. The range of the height h is within the range from 0 to ⅕ of the maximum outer diameter of the lens.

The surface distance is obtained by measurement using a central thickness and surface spacing measurement device, OptiSurf (available from Trioptics), for length measurement of an assembled lens.

The refractive index is obtained by measurement using a precision refractometer, KPR-2000 (available from Shimadzu Corporation), with a subject temperature of 25° C. A refractive index measured with respect to the d-line the wavelength of 587.6 nm) is a refractive index Nd. Similarly, a refractive index measured with respect to the e-line (the wavelength of 546.1 nm) is a refractive index Ne, a refractive index measured with respect to the F-line (the wavelength of 486.1 nm) is a refractive index NF, a refractive index measured with respect to the C-line (the wavelength of 656.3 nm) is a refractive index NC, and a refractive index measured with respect to the g-line (the wavelength of 435.8 nm) is a refractive index Ng. The Abbe number νd with respect to the d-line is obtained by calculating νd=(Nd−1)/(NF−NC) by substituting the values of Nd, NF and NC obtained by the above-described measurement into the equation. 

What is claimed is:
 1. An imaging lens consisting of five lenses consisting of, in order from an object side: a first lens having a positive refractive power with a convex surface toward the object side; a second lens having a negative refractive power and having a meniscus shape with a convex surface toward the image side in the vicinity of the optical axis; a third lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; a fourth lens having a positive refractive power and having a meniscus shape with a convex surface toward the image side; and a fifth lens having a negative refractive power, wherein an image-side surface of the fifth lens includes a concave surface and at least one inflection point, wherein the conditional expression below is satisfied: 1.15<f/f1<1.7  (1), where f is a focal length of the entire system, and f1 is a focal length of the first lens.
 2. The imaging lens as claimed in claim 1, wherein the conditional expression below is further satisfied: −1.48<f/f45<0  (2), where f45 is a combined focal length of the fourth lens and the fifth lens.
 3. The imaging lens as claimed in claim 2, wherein the conditional expression below is further satisfied: −1.25<f/f45<0  (2-1), where f45 is a combined focal length of the fourth lens and the fifth lens.
 4. The imaging lens as claimed in claim 3, wherein the conditional expression below is further satisfied: −1.1<f/f45<−0.05  (2-2), where f45 is a combined focal length of the fourth lens and the fifth lens.
 5. The imaging lens as claimed in claim 1, wherein the conditional expression below is further satisfied: −1.5<f12/f45<0  (3), where f12 is a combined focal length of the first lens and the second lens, and f45 is a combined focal length of the fourth lens and the fifth lens.
 6. The imaging lens as claimed in claim 5, wherein the conditional expression below is further satisfied: −1.45<f12/f45<−0.05  (3-1), where f12 is a combined focal length of the first lens and the second lens, and f45 is a combined focal length of the fourth lens and the fifth lens.
 7. The imaging lens as claimed in claim 1, wherein the conditional expression below is further satisfied: −0.3<f/f345<0.35  (4), where f345 is a combined focal length of the third to the fifth lenses.
 8. The imaging lens as claimed in claim 7, wherein the conditional expression below is further satisfied: −0.29<f/f345<0.2  (4-1), where f345 is a combined focal length of the third to the fifth lenses.
 9. The imaging lens as claimed in claim 1, wherein the conditional expression below is further satisfied: −0.95<f/f2<−0.65  (5), where f2 is a focal length of the second lens.
 10. The imaging lens as claimed in claim 9, wherein the conditional expression below is further satisfied: −0.9<f/f2<−0.68  (5-1), where f2 is a focal length of the second lens.
 11. The imaging lens as claimed in claim 1, wherein the first lens has a meniscus shape.
 12. The imaging lens as claimed in claim 1, further comprising an aperture stop disposed on the object side of the object-side surface of the second lens.
 13. The imaging lens as claimed in claim 1, wherein the fifth lens has a biconcave shape.
 14. The imaging lens as claimed in claim 13, wherein the conditional expression below is further satisfied: 0.05<f/f3<0.95  (6), where f3 is a focal length of the third lens.
 15. The imaging lens as claimed in claim 14, wherein the conditional expression below is further satisfied: 0.06<f/f3<0.9  (6-1), where f3 is a focal length of the third lens.
 16. The imaging lens as claimed in claim 13, wherein the conditional expression below is further satisfied: 0.48<f/f4<1.57  (7), where f4 is a focal length of the fourth lens.
 17. The imaging lens as claimed in claim 16, wherein the conditional expression below is further satisfied: 0.5<f/f4<1.56  (7-1), where f4 is a focal length of the fourth lens.
 18. The imaging lens as claimed in claim 1, wherein the conditional expression below is further satisfied: 1.22<f/f1<1.6  (1-1).
 19. The imaging lens as claimed in claim 18, wherein the conditional expression below is further satisfied: 1.25<f/f1<1.55  (1-2).
 20. An imaging device comprising the imaging lens as claimed in claim
 1. 